The present invention is related to Japanese patent application No. Hei. 11-57896, filed Mar. 5, 1999; No. Hei. 11-298636, filed Oct. 20, 1999; No. Hei. 11-301608, filed Oct. 22, 1999; No. Hei. 11-330583, filed Nov. 19, 1999; No. Hei. 11-330489, filed Nov. 19, 1999; No. Hei. 11-200906, filed Jul. 14, 1999; and No. Hei. 11-200966, filed Jul. 14, 1999; the contents of which are incorporated herein by reference.
The present invention relates to a boiling and cooling apparatus for transferring heat from a heating body, and more particularly, to a boiling and cooling apparatus for transferring heat which reduces burnout, increases cooling tank rigidity and increases heat transfer performance.
Presently, boiling and cooling systems have been constructed to cool components, such as IGBT modules. One such system is disclosed in Japanese Patent Application Laid Open No. 8-78588. As shown in FIG. 5, this boiling and cooling apparatus includes a refrigerant tank 100 for reserving a liquid refrigerant and a radiator 110 disposed over the refrigerant tank 100. In the radiator 110, corrugated inner fins 120 are provided which are offset to the left side, as shown. As a result of this construction, refrigerant vapor is first boiled by heat from heating body 130. The boiled refrigerant rises in passage 140, after formation on the right side of inner fins 120 in radiator 110. The vapor flows into upper space 150 in radiator 110, where it is cooled into a condensed liquid by an external fluid, until it can be recirculated into the refrigerant tank 100 via the internal passages of the inner fins 120.
While this device provides cooling to a selected component, there exist some drawbacks with respect to its operation. Specifically, in the aforementioned boiling and cooling apparatus, the lower end opening of the radiator 110 and the upper end opening of the refrigerant tank 100 communicate with each other over their entire faces. As a result, refrigerant vapor, boiled in refrigerant tank 100, is blown up to the lower end face of inner fins 120 and interferes with the condensed liquid flowing down in the internal passages of the inner fins 120. This impedes refrigerant circulation.
Another such invention is disclosed in Japanese Patent Application Laid-Open No. 8-236669. In this cooling apparatus, as shown in FIG. 3, the boiling area in a refrigerant tank 100 is increased to improve radiation performance. This increase in boiling area is accomplished by arranging fins 120 proximate the boiling face in the refrigerant tank 100, thereby receiving the heat of the heating body 110 mounted to the surface of the refrigerant tank 100.
To accomplish this task, fins 120 are arranged in the refrigerant tank 100 to form a plurality of passage portions 130, in which the vaporized refrigerant (or bubbles) rise. Some of the individual passage portions 130 have more or less bubbles than the remainder. The number of bubbles in each passage is dependant upon the position of the heating portion of heating body 110 with respect to the passage. The higher the position of passage portions 130 toward the radiator, the more the number of bubbles increases. As such, the small bubbles join together to form larger bubbles. In the passages containing a large number of bubbles, the boiling faces are typically covered with bubbles, thereby lowering the boiling heat transfer coefficient. As a result, it is possible that the boiling face may undergo an abrupt temperature rise (or burnout).
This problem is excentuated even more when the fin pitch is reduced to retain a larger boiling area. In such an instance, the passage portions 130 have reduced open areas and are almost filled with the bubbles. This seriously reduces the quantity of refrigerant flowing through the system, making burnout on the boiling faces highly probable.
Another boiling and cooling device is disclosed in Japanese Patent Application No. 11-200966 (assigned to the assignee of the present invention). Here, a boiling and cooling apparatus is proposed, in which the ribs are provided on only the side of the inner wall, proximate to the heating body, and clearances are provided at their leading ends.
While this device does provide an increased radiation area, it is still desirable to obtain a larger radiation area, especially for increased heat load due to increased heat flux. Moreover, if the ribs are made of an extrusion molding to reduce cost, it is difficult to make a finer rib structure to increase the radiation area, resulting in an inability to cope with a higher heat flux.
Likewise, another, such boiling and cooling apparatus is disclosed in Japanese Patent Application Laid-Open No. 9-167818. This boiling and cooling apparatus includes a refrigerant tank made of an extruded member. An IGBT module acts as the heating body, and is mounted on the surface of the refrigerant tank. On its inside, the refrigerant tank is divided into a plurality of passage-shaped spaces 130, as shown in FIGS. 4 and 8, by ribs 110. As shown, ribs 110 are formed on extruded member 100.
While this device does provide boiling and cooling functions, it has several drawbacks. Here, the IGBT module does not have a uniform radiation temperature all over its radiation area to contact with the surface of the refrigerant tank. Instead, this device provides a temperature distribution transversely (or in the horizontal direction of FIG. 4) in the refrigerant tank. With the inside of the refrigerant tank being divided into the plurality of passages by the ribs 110, the bubbling rates are different among the individual passages, thereby providing a higher number of bubbles in passages 120 and a lower number of bubbles in passages 130, as shown in FIG. 4. As a result, burnout occurs in the more bubbled passages 120, thereby reducing radiation performance. This problem arises most often when the radiation of the heating body increases, especially when the amount of refrigerant in the refrigerant tank is lowered, or thinned to reduce cost.
Moreover, another problem arising with respect to Japanese Patent Application Laid-Open No. 9-167818 involves the mounting of the refrigerant tank 100. When the heating body 110 is mounted on only one side (or one surface) of the refrigerant tank 100, the ribs 120 become lower in temperature as they get further away from the heating body mounting side. This is graphically illustrated in FIG. 2. In the non-boiling region, the boiling overheat drops to provide no effective boiling region. As a result, in the non-boiling region of the ribs 120, ribs 120 do not increase the radiation area. However, the presence of the ribs 120 obstructs the boiling flow (or the flow of bubbles) rising in the refrigerant tank 100 and may cause the burnout.
Also, as illustrated in FIG. 1, the sectional area of each hollow portion is reduced because the vigorous boiling region 210 is defined into the plurality of hollow portions 160. As radiation increases the amount of bubbling, the boiling faces forming hollow portions 160 are covered with bubbles. As a result, the temperature of the boiling faces may abruptly rise to cause burnout.
Systems have been devised to overcome the above-discussed as well as other overheating problems. Such systems include providing a boiling and cooling device which increases its boiling area by forming a porous layer in the boiling portion. Refrigerants can be used, such as freon or the like, which have a low surface tension and therefore easily wet a surface. In this instance, a bubbling point structure as small as about several microns is required for stabally producing bubble nuclei necessary to boil the refrigerant. However, the machining required to produce such a small bubbling point structure is seriously difficult to manufacture. Moreover, the cost of such an endeavor is extremely high, thereby reducing its practicality. The present invention was developed in light of these drawbacks.
It is therefore an object of the present invention to provide a boiling and cooling apparatus, which improves radiation performance by promoting the refrigerant circulation in the radiator by providing an entrance and exit flow path for the refrigerant.
It is yet another object of the present invention to provide a boiling and cooling apparatus, which improves the burnout resistance by providing ribs for increasing the radiation area of the refrigerant tank.
It is another object of the present invention to provide a boiling and cooling device having an intermediate wall portion to divide the refrigerant tank into a region which has a higher temperature and a region which has a lower temperature to isolate the differing boiling regions.
A boiling and cooling apparatus is provided which has a refrigerant tank for maintaining a liquid refrigerant for boiling when it receives heat from a heating body, a radiator which receives refrigerant vapor boiled in the refrigerant tank. The radiator cools refrigerant vapor to form the liquid refrigerant by exchanging heat with an external fluid. The radiator includes a first passage for receiving the refrigerant vapor and a second passage for returning condensed liquid to the refrigerant tank. The radiator has an upper space which provides communication between the first passage and the second passage, whereby the refrigerant vapor is guided to flow preferentially into the first passage.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are intended for purposes of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.